Introduction: Structured physical activity may improve physical, cognitive, and social functionality, as well as overall quality of life of people with high-grade glioma. Yet, engaging them in such activities remains highly challenging due to their unique disease burden and perceived “loss of control.” A greater understanding of patients’ interests, preferences, behavioral motivations, and perceived barriers around physical activity is needed to design tailored and patient-led physical activity interventions. This protocol describes the method and ethical considerations of a cross-sectional mixed-methods study that has been developed to collect such information from glioma patients and their carers. Methods and analysis: The International Physical Activity Questionnaire (IPAQ 7, short form) and semi-structured interviews will be used for data collection. IPAQ scoring protocol will be followed to examine objective data and Clarke and Braun’s thematic approach will be used to analyze the interview transcripts. Ethics: Ethical approval was obtained from Cardiff University’s Research Ethics Committee and from the regional NHS Research Ethics Committee. The main ethical concerns are to maintain patients’ safety and comfort and ensure that their consent remains informed and valid throughout the recruitment, data collection, management, and dissemination stage. Risks associated with their physical condition, emotional distress, and time commitment should be continuously assessed and necessary actions should be taken accordingly. Conclusion: The protocol will work as a step by step guide for future researchers for developing similar qualitative research and obtaining ethical approval when involving vulnerable individuals like high-grade glioma patients in studies.